There was a thread on this on GD in November, but judging from some of the bottom 25 lists from those who contributed to it, this episode seems to have gone down in quite a few people's estimation since then (if that is possible). Anyway, my review:
In addition to having lousy jokes, possibly the emptiest Bart/Lisa conflict ever and a plot with barely even the vaguest semblance of a point or purpose, this is probably the most lazily written episode ever. Little or nothing is done with the future setting, with most characters just vaguely changing their appearances with the same voices as before (to hear the 38 year old Ralph still talking like a retarded second-grader is particularly painful, and even Bart looks more like a lazy college student than a 40 year old), the script is unimaginative using the same tired recurring jokes ("Smell ya later", "Relax, you'll live longer", "Dude", "You used to be cool") and the main storyline consists of essentially little more than OFF and other Springfieldians in the same setting as other present-day episodes (albeit 30 years later) without the wonderfully imaginative futuristic gags that made Lisa's Wedding so compelling, with the added gimmick of Lisa as president and Bart as a drunken loser (hardly innovative stuff).
And people who think it is being unfairly derided by comparing it to Lisa's Wedding are missing the point. Even without that classic it would still be regarded as a pretty crappy episode on its own merits (or lack of), and the very fact that Lisa's Wedding was made is emblematic of just how unoriginal and uninspired this episode is, basically recycling previous elements from its predecessor - Lisa being successful, Bart in some dead-end job, the ending with Lisa and Bart walking off in the sunset being an almost exact replica of the Homer/Lisa ending (which was, needless to say, infinitely more touching) - without adding anything meaningful or even funny.
So, while not the worst episode ever (KTAAR, Alone Again, Natura-Diddly, The Mansion Family and A Tale of Two Springfields are worse than this IMO), a definite bottom 10 contender.
(Cue people springing to its defence and saying "it's not actually that bad", "3/5", etc.)